A liquid crystal display (LCD) is a type of flat panel display (FPD), which shows images by the property of liquid crystal material. Comparing with other display devices, the liquid crystal display has advantages in lightweight, compactness, low driving voltage and low power consumption, and thus has already become the mainstream product in the whole consumer market. However, the liquid crystal material of the liquid crystal display cannot emit light by itself, and must depend upon an external light source. Thus, the liquid crystal display further has a backlight module to provide the needed light source.
Generally, the backlight module can be divided into two types, i.e. the side-light type backlight module and the direct-light type backlight module. Traditional backlight modules mainly use cold cathode fluorescent lamps (CCFLs), hot cathode fluorescent lamps (HCFLs) or semiconductor emitting diodes as light sources, wherein the semiconductor emitting diodes mainly use light emitting diodes (LEDs) to emit light. In comparison with the cathode fluorescent lamps, the light emitting diodes can save more electric power, have longer lifetime, and more compact volume, so that there is a trend to gradually use the light emitting diodes to replace the cathode fluorescent lamps.
Nowadays, an LED is generally in form of chip to be assembled into a semiconductor package, i.e. an LED package structure, which is finally connected to a fixed plate of a backlight module. Product types of the LED package structures are classified according to condition features including light colors, chip material, luminance, size and etc. A single chip generally can construct a point type light source, while a plurality of assembled chips can construct a surface type light source or a linear type light source for the purpose of signaling, indicating status, or displaying. The light emitting display is constructed by a plurality of chips suitably connected (in series or in parallel) and suitable optical structures, all of which construct light emitting sections and light emitting points of the light emitting display. Furthermore, a surface-mounting-device type LED (SMD-LED) is attached to a surface of a circuit board, so that it is suitably applied to a SMT (surface mounting technology) process for carrying out reflowing. Thus, it can efficiently solve problems of brightness, visual angle, evenness, reliability, uniformity and etc. Moreover, the SMD-LED is used with lighter material of a PCB board and a reflective layer, and omitted terminals made of carbon steel in a dip type LED, so that epoxy resin filled in a display reflective layer can be reduced, and a half of product weight of the SMD-LED can be easily removed to finally optimize the application thereof. Thus, the SMD-LED gradually replaces the terminal type LED, and can provide more flexible designs, especially occupying a market share in the LED display market and having a trend of rapidly developing.
Referring now to FIG. 1, a cross-sectional view of a traditional LED package structure is illustrated. As shown in FIG. 1, a traditional LED package structure 90 comprises a housing 91, a first electrode plate 92, a second electrode plate 93, an LED chip 94 and a transparent encapsulant 95. An upper surface of the housing 91 is formed with a recess 911. A portion of the first electrode plate 92 is disposed on the bottom of the recess 911, and the other portion thereof is extended out of the housing 91 for being electrically connected with an external power supply. A portion of the second electrode plate 93 is disposed on the bottom of the recess 911, and the other portion thereof is extended out of the housing 91 for being electrically connected with an external power supply. The LED chip 94 has a first electrode (not-shown) and a second electrode (not-shown). The LED chip 94 is disposed in the recess 911, wherein the first electrode is electrically connected with the first electrode plate 92, and the second electrode is electrically connected with the second electrode plate 93 through a first wire 96. The transparent encapsulant 95 encapsulates the recess 911 and covers the components in the recess 911, wherein the light of the LED 94 can emit upward through the transparent encapsulant 95.
In the traditional LED package structure 90, the design of the housing 91 should have an ideal transparent encapsulant 95 with a horizontal surface. However, due to the shrinkage of the material of the transparent encapsulant 95 after hardening and the surface tension action on the surface of the transparent encapsulant 95 enclosed by the edge of the recess 911 of the housing 91, a central portion of the surface of the transparent encapsulant 95 is actually in a recessed status. Because the refractive index of the transparent encapsulant 95 is greater than that of the air, a portion of light will be total reflected when the light passes through an interface between the surface of the transparent encapsulant 95 and the air. Even though the light of total reflection is reflected from walls of the recess 911 and then emits out of the transparent encapsulant 95, the light still will be attenuated to affect the light extraction efficiency.
Referring now to FIG. 2, a cross-sectional view of another traditional LED package structure is illustrated. As shown in FIG. 2, the LED package structure 90′ of FIG. 2 is substantially the same as the LED package structure 90 of FIG. 1, and the difference between the two traditional LED package structures 90 and 90′ is that: the transparent encapsulant 95′ of the LED package structure 90′ of FIG. 2 has a design of a convex lens. Thus, it can prevent from the attenuation condition due to the total reflection of the light, as described above, while the light can be efficiently emitted outward with a greater visual angle. However, it will relatively increase the manufacture cost of the transparent encapsulant 95′. Meanwhile, because the transparent encapsulant 95′ is protruded from the housing 91′, it is disadvantageous to execute the following SMT or other manufacturing processes of the LED package structure 90′.
As a result, it is necessary to provide an LED package structure to solve the problems existing in the conventional technologies, as described above.